Repair of channels between well bores



Oct. 31, 1967 J w, R ET AL 3,349,844

REPAIR OF CHANNELS BETWEEN WELL BORES Filed July 8, 1964 2 Sheets-Sheet 1 INJECTION WELL |OO/ WATERJ 1' WATER s 1 FIG. I. 27

R ECOVERY WELL INITIAL FLOODED AREA '9 FLUID H '3 l7 BREA/K-THRU /23 43 mmcA'roR FLUID CONTAINING H RADIOACTIVE TRACER \u DETECTOR 1- INVENTQRS. JOHN w. RHEA, JOE v. MORSE,

ATTORNEY.

Oct. 31, 1967 J. w. RHEA ET AL 3,349,844

REPAIR OF CHANNELS BETWEEN WELL BORES Filed July 8, 1964 2 Sheets-Sheet 2 INDICATOR FLUID FIG. 3- 5 I 2.7 a z Y H REPAIR FLUID NORMAL T OIL RECOVERY,

FLOO AREA BREAK'THRU REPAIRED INVENTORS. JOHN w. RHEA,

JOE v. MORSE,

{EBM

AT TORNEYL United States Patent 3,349,844 REPAIR OF CHANNELS BETWEEN WELL BORES John W. Rhea and Joe V. Morse, Monahans, Tex., assignors, by mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed July 8, 1964, Ser. No. 381,192 5 Claims. (Cl. 166-4) This invention relates generally to secondary recovery operations, and more particularly to a technique for repairing channels between well bores that deleteriously affect secondary recovery operations for recovering oil and gas deposits from earth formations.

When the primary energy of an oil or gas reservoir in the earth has been spent, it is customary to institute secondary recovery operations wherein a fluid under pressure is injected into the earth from a first well bore, and earth fluids are withdrawn from the reservoir to a second well bore. The secondary recovery fluid may be a gas or may be water. When water is used, various chemicals may be added thereto for the purpose of compensating for characteristics of the earth formations that may deleteriously affect the secondary recovery operations.

From time to time premature breakthrough of injected fluids into at producing well has been experienced during secondary recovery operations. Such breakthroughs are caused bychannels between the well bores that permit direct fluid communication therebetween. Such channels either may be normally occurring or may be fractures in the earth produced as the result of the application of excessively high injected fluid pressures. Such fractures have been experienced most often in certain West Texas fields Where there are a number of pressure-sensitive planes in formations. The Sand Belt Trend fields in the area of Monahans, Tex., contain a number of such planes.

In the past attempts have been made to repair such channels by pumping plugging materials such as cementitious mixtures into the channels. Such attempts have been unsuccessful for the most part.

In accordance with the teachings of the present invention, there is formed at the earths surface a preparatory or indicator fluid having an apparent viscosity of at least 30 centipoises at 30 0 rpm. on a Faun viscosimeter and a water loss of no more than 20 cc. A'PI. Also, there is prepared a cementitious mixture having a water loss no more than 60 cc. API. Preferably, the first one-half of the indicator fluid is radioactive such that its radioactivity is at least 0.1 to 0.5 millicurie per barrel. (The term barrel as used herein designates the standard 42 US. gallon barrel commonly used as a measure in oil field practice.) The indicator fluid is pumped into the fracture through the first well bore ahead of the cementitious mixture. Preferably, the volume of the indicator fluid is at least equal to the volume of liquid in the first well bore between the earths surface and the level of the channel opening into the first well bore during the repair operations. The arrival of the fluid at a predetermined location in the second well bore is detected to determine the volume of the channel between the well bores. Preferably, this is accomplished by positioning a radioactivity detector at a given level in the second well bore, such as in the vicinity of the opening of the channel into the second well bore, so that a change in the radioactivity detected thereby will signify the arrival of the indicator fluid at the given level in the second well bore. After detection of the fluid, additional cementitious mixture is pumped into the channel until the indicator fluid is displaced from the channel and the cementitious mixture substantially fills the channel. Subsequent injection of secondary recovery fluids into the formation through the first well bore is delayed until the cementitious mixture has hardened.

Objects and features of the invention not apparent from the foregoing discussion will become evident upon consideration of the following detailed description thereof taken in connection with the accompanying drawings wherein FIGS. 1, 2, 3, and 4 are eiementary, simplified schematic diagrams of well installations and associated apparatus for use in connection with the invention, for the purpose of illustrating various steps of the invention.

With reference now to the figures generally, and particularly to FIG. 1, there is shown a cased well bore 7 extending from the earths surface 1 to the level of a hydrocarbon-containing earth formation 11. A tubing string 3 extends through the well bore from the earths surface to the level of formation 11 within the casing, and a production packer 13 is used to close the annulus between the tubing and the casing so that fluid pressure can be exerted below packer 13 through tubing string 3. The customary well head apparatus is not shown in order to avoid unnecessarily cluttering the drawing. A valve 5 is illustrated which controls the flow of fluid through tubing string 3. The tubing string connected to a pump (not shown) for the purpose of injecting secondary recovery fluids into the tubing string 3 under pressure.

The casing is illustrated as having a number of perforations 15 below the level of packer 13 for the purpose of providing fluid communication between the well bore below packer 13 and formation 11. A production or recovery well 22 spaced apart from the injection well is provided with a casing string 23 which may be cemented to the walls of the borehole in the usual manner, and a tubing string 25 controlled by valve 27 for the purpose of conducting produced fluids from formation 11 to the earths surface. The tubing string 25 may or may not be provided with a production packer 29, and the casing string 23 is perforated by perforations 31 as is customary.

In FIG. 1, a secondary recovery fluid, such as suitably treated Water, is shown as being injected into tubing string 3 through perforations 15 into formation 11. A channel or fracture 17 through the formation from one of the perforations 15 to one of the perforations .31 provides a path for direct fluid flow between the two well bores. This channel may be a fracture formed after initially flooded area 19 has been swept by the secondary recovery fluid as the result of the required secondary recovery fluid pressure having been sufficiently great to fracture the formation along a plane of weakness thereof, or may be caused by hydraulic fracturing when completing or stimulating the well. The secondary recovery fluid 21 will follow the path of least resistance and will flow from borehole 7 to borehole 22 through channel 17 rather than flowing through the interstices of formation 11. While the fracture is shown as having occurred in a horizontal plane, it is to be understood that the fracture may have occurred along a vertical plane or along a tilted plane, or may have varied between various angles of inclination as it was propagated through the formation.

As stated above, to repair the formation damage, initially there is formed at the earths surface an indicator fluid 43 having an apparent viscosity of at least 30 centipoises at 300 rpm. on a Fann viscosimeter and a water loss of no more than 20 cc. API. This indicator fluid may comprise either an aqueous or non-aqueous carrier fluid such as water, lease oil, diesel oil, or other suitable, commonly available fluids. For the purpose of increasing the viscosity thereof and reducing the water loss, an organic colloidal water loss agent is mixed therewith. The water loss agent may be either a hydrophilic organic colloidal agent such as starch, carboxymethyl cellulose, hydroxy- 3 at its upper end is ethyl cellulose, guar flour, gum tragacanth, Irish moss, and albumin, or an oleophilic organic colloidal agent such as uncured butyl rubber, uncured polypropylene, uncured butadiene polymer, uncured polystyrene, uncured natural rubber, and blown asphalt. Manifestly, a hydrophilic organic colloidal agent will be used when an aqueous carrier fluid is used, and an oleophilic organic colloidal agent Will be used when a non-aqueous carrier fluid is used. Of the above, guar flour is preferred as the thickening and water loss control agent. Preferably, between 20 and 40 pounds of the preferred thickening and water loss control agent is used per 1000 barrels of carrier fluid, according to depth and formation temperature.

In a preferred embodiment of the invention, there is added to the carrier fluid and water loss control agent a sufficient amount of a radioactive material to produce a radioactivity of at least 0.1 millicurie per barrel of the mixture, according to expected dilution. The radioactive materials should have a half life of at least one day, suflicient so that a detectable and measurable amount of radioactivity will remain in the fluid after a time interval equal to the interval required for the liquid to traverse the distance between the well bores through the channel therebetween, as described hereinafter. The most desirable radioactive agent for this purpose is iodine soluble in oil or water. However, other radioactive materials may be used.

There is also formed at the earths surface a cementitious mixture which may be any of the cements commonly used in oil field practice for the purpose of bonding casing strings to surrounding earth formations. However, other materials may be used, such as materials that will pack in the channel to form a relatively solid impermeable mass. Such a material can be granulated calcium carbonate having a particle size no greater than 200 mesh. It is preferable, however, to use a cementitious mixture. To the cementitious mixture, other fracture control fluid is added to a hydrophilic water loss control agent, such as one of the colloidal agents described above or other commonly used water loss control agents for cementitious mixtures, sufficient in amount to reduce the water loss of the mixture to no more than 60' cc. API.

In FIG. 2 there is shown a radioactivity detector 41 lowered through tubing string 25 to the level of channel 17 between the well bores. The radioactivity detector 41 is suspended on a cable 39 about a sheave 37. Cable 3% is reeled on a reel 35 having an electrical connection 34 to an electrical indicating device 33. The electrical connection extends from the indicating device 33 to the radioactivity detector 41 so that electrical output signals are transmitted to indicator 33 so that an operator at the earths surface will be able to ascertain the radioactivity being detected by detector 41 in accordance with the amplitude of the electrical signals indicated by indicator 33. The indicator fluid 43 described above containing the radioactive agent is illustrated as being pumped through tubing string 3 into the fracture or channel 17 to displace the secondary recovery fluid 21 through channel 17 into the recovery Well bore 22 and out the tubing string 25. When the indicator fluid 43 arrives at the recovery well bore 22 the electrical signal produced by detector 41 will indicate a substantial increase in the radioactivity being detected thereby. The indicator fluid should be at least equal in volume to the volume of tubing string 3 and the space below packer 13, and may be greater than this volume if desired. The volume of the indicator fluid injected into the tubing string 3 is measured, as is the volume of the cementitious mixture therebehind. Preferably, the volumetric measurement is continuous rather than batchwise. The cementitious mixture is injected into tubing string 3, as illustrated in FIG. 3, to displace the indicator fluid 43 through the fracture. Inasmuch as the volume of tubing string 3 and the space therebelow is known, and inasmuch as the volume of the injected fluids is known by virtue of the detection of the arrival of indicator fluid 43 at recovery well bore 22 by detector 41, the volume of cement required to fill the channel or opening 17 can now be ascertained. An additional quantity of cement is injected into the channel or fracture 17 to displace the indicator fluid 43 into recovery well bore 22. Preferably, valves 27 and 5 are now closed, the fracture is kept under pressure, and cement will not be squeezed therefrom into the well bores. After the cement has hardened, conventional waterflooding operations may again commence. It may be necessary to circulate any additional cement out of injection well bore 7 in the usual manner and, if the perforations are plugged with cement, it also may be necessary to reperforate the injection Well bore.

In connection with the invention, it should be noted that where fractures are vertically inclined, the detector 41 should be positioned at a sufliciently high level in recovery well bore 22 that the entire volume of the fracture will be filled with indicator fluid 43 when the arrival of the indicator fluid at a given level in the Well bore 22 is detected. This is no problem, however, inasmuch as the volume of the well bore below the level of the radioactivity detector is known. In order to prevent an unnecessary number of perforations 15 from being plugged by cement, it may be desirable to position a bridge plug below the perforation in communication with channel 17, or to position a straddle packer above and below such perforation or perforations.

Other techniques of detecting the arrival of the indicator fluid at a given level in the well bore may be used, such as detecting the arrival of the indicator fluid at the earths surface by incorporating a quantity of ammonium thiocyanate in the indicator fluid and periodically adding a few drops of concentrated ferric chloride solution to the sample of the fluid issuing from tubing string 25 until a color change occurs. This latter technique is described in an article by J. L. Boyd et al. appearing in the periodical World Oil, September 1962, page 68.

Having described the principle of the invention and the best mode contemplated for applying that principle, it is to be understood that the apparatus described is illustrative only and that other means can be employed without departing from the true scope of the invention.

What is claimed is:

1. In the secondary recovery of hydrocarbons from a subsurface earth formation wherein a fluid is injected into the formation through a first well bore and connate earth fluids are withdrawn through a second well bore spaced apart therefrom, a method of repairing the formation when a channel therein permits direct fluid communication between the well bores, comprising:

forming a fluid having an apparent viscosity of at least 30 centipoises, a Water loss of not more than 20 cc. API, and a radioactivity of at least 0.1 millicurie per 42-gallon barrel of a radioactive material having a half life of at least one day;

positioning a radioactivity detector in the second well bore in the vicinity of the intersection of the channel and said second well bore;

pumping a quantity of said fluid into said channel through said first well bore ahead of a cementitious mixture including an organic colloidal water loss additive;

measuring the quantity of said fluid and of said cementitious mixture pumped into said first well bore; with said detector, detecting the intrusion of said fluid into said second well bore;

after detection of said fluid, pumping an additional quantity of said cementitious mixture into said formation to fill a substantial percentage of volume of the channel;

removing excess cementitious mixture from said first well bore; and

preventing egress of further amounts of fluid from said second well bore and placing said first well bore, said channel, and said second well bore under hydraulic pressure until said cementitious mixture has hardened.

2. In the secondary recovery of hydrocarbons from a subsurface earth formation wherein a fluid is injected into the formation through a first well bore and connate earth fluids are withdrawn through a second Well bore spaced apart therefrom, a method of repairing the formation when a channel therein permits direct fluid communication between the well bores, comprising:

forming a fluid having an apparent viscosity of at least 30 centipoises and a water loss of not more than 20 cc. API; pumping a quantity of said fluid into said channel through said first well bore ahead of a cementitious mixture having a Water loss no greater than 20 cc. A'PI; measuring the quantity of said fluid and of said cementitious mixture pumped into said channel; detecting the arrival of said fluid at a predetermined location in said second Well bore to determine the volume of the channel;

after detection of said fluid, pumping said cementitious mixtures into said channel until said fluid is displaced from said channel and the cementitious mixture substantially fills the channel; and delaying subsequent injection of secondary recovery fluid into said formation through said first well bore until the cementitious mixture has hardened. 3. In the secondary recovery of hydrocarbons from a subsurface earth formation wherein a fluid is injected into the formation through a first well bore and connate earth fluids are withdrawn through a second well bore spaced apart therefrom, a method of repairing the formation when a channel therein permits direct fluid communication between the well bores, comprising:

forming a fluid having an apparent viscosity of at least 30 centipoises and a Water loss of not more than 20 cc. API comprising a carrier fluid and an organic colloidal water loss agent;

pumping a quantity of said fluid into said channel through said first well bore at least equal in volume to the volume of liquid in the Well bore between the earths surface and the level of the channel opening into said first well bore;

following said fluid with a cementitious mixture including an organic colloidal water loss agent suflicient in quantity to reduce the water loss of said cementitious mixture to no more than 60 cc. API;

measuring the quantity of said fluid and of said cementitious mixture pumped into said channel;

detecting the instrusion of said fluid into said second well bore;

pumping an additional quantity of said cementitious mixture into said channel to fill a substantial percentage of the channel; and

delaying subsequent injection of secondary recovery fluid into said formation through said first well bore until the cementitious mixture has hardened.

4'. In the secondary recovery of hydrocarbons from a subsurface earth formation wherein a fluid is injected into the formation through a first well bore and connate earth fluids are withdrawn through a second well bore spaced apart therefrom, a method of repairing the formation when a channel therein permits direct fluid communication between the well bores, comprising:

forming a fluid having an apparent viscosity of at least 30 centipoises, a water loss of not more than 20 cc. API, and a radioactivity of at least 0.1 millicurie per 42-gallon barrel of a radioactive material having a half life of at least one day;

positioning a radioactivity detector in the second well bore in the vicinity of the intersection of the channel and said second well bore; pumping a quantity of said fluid. into said channel through said first well bore ahead of a cementitious mixture having a water loss no greater than 60 cc. API,

and concomitantly withdrawing fluids from said second well bore; measuring the quantity of said fluid and of said cementitious mixture pumped into said channel; with said detector, detecting the intrusion of said fluid into said second well bore; after detection of said fluid, pumping into said channel an additional quantity of said cementitious mixture substantially equal in volume to the volume of said channel; and preventing egress of further amounts of fluid from said second well bore to place said first Well bore, said channel, and said second well bore under hydraulic pressure until said cementitious mixture has hardened. 5. In the secondary recovery of hydrocarbons from a subsurface earth formation wherein a fluid is injected into the formation through a first Well bore and connate earth fluids are withdrawn through a second well bore spaced apart therefrom, a method of repairing the formation when a channel therein permits direct fluid communication between the well bores, comprising:

forming a fluid having an apparent viscosity of at least 30 centipoises, a water loss of no more than 20 cc. API, and a radioactivity of at least 0.1 millicurie per 42-gallon barrel of a radioactive material having a half life at least equal to the estimated time for a fluid interface to traverse the earth formation between said Well bores through said channel; positioning a radioactivity detector in the second well bore in the vicinity of the intersection of the channel and said second well bore; pumping a quantity of said fluid into said channel through said first well bore ahead of a cementitious mixture including an organic colloidal water loss additive suflicient to reduce the water loss of the cementitious mixture to no more than 60 cc. API, and concomitantly withdrawing fluids from said second well bore; measuring the quantity of said fluid and of said cementitious mixture pumped into said channel, the volume of said fluid pumped into said channel being at least equal to the volume of liquid in the Well bore between the earths surface and the level of the channel opening into said first well bore; with said detector, detecting the intrusion of said fluid into said second Well bore; after detection of said fluid, pumping an additional quantity of said cementitious mixture into said channel substantially equal to the volume of said fluid to displace said fluid from said channel; and preventing egress from said second well bore of further amounts of fluid and placing said first Well bore, said channel, and said second well bore under hydraulic pressure until said cementitious mixture has hardened.

References Cited UNITED STATES PATENTS 2,869,642 1/1959 McKay et al. 166-4 3,003,856 10/1961 Boyd l66--4 X 3,198,249 8/1965 Willman 1664 STEPHEN I. NOVOSAD, Primary Examiner. 

2. IN A SECONDARY RECOVERY OF HYDROCARBONS FROM A SUBSURFACE EARTH FORMATION WHEREIN A FLUID IS INJECTED INTO THE FORMATION THROUGH A FIRST WELL BORE AND CONNATE EARTH FLUIDS ARE WITHDRAWN THRUGH A SECOND WELL BORE SPACED APART THEREFROM, A METHOD OF REPAIRING THE FORMATION WHEN A CHANNEL THEREIN PERMITS DIRECT FLUID COMMUNICATION BETWEEN THE WELL BORES, COMPRISING: FORMING A FLUID HAVING AN APPARENT VISCOSITY OF AT LEAST 30 CENTIPOISES AND A WATER LOSS OF NOT MORE THAN 20 CC. API; PUMPING A QUANTITY OF SAID FLUID INTO SAID CHANNEL THROUGH SAID FIRST WELL BORE AHEAD OF A CEMENTITIOUS MIXTURE HAVING A WATER LOSS OF GREATER THAN 20 CC. API; MEASURING THE QUANTITY OF SAID FLUID AND OF SAID CEMENTITIOUS MIXTURE PUMPED INTO SAID CHANNEL; DETECTING THE ARRIVAL OF SAID FLUID AT A PREDETERMINED LOCATION IN SAID SECOND WELL BORE TO DETERMINE THE VOLUME OF THE CHANNEL; AFTER DETECTION OF SAID FLUID, PUMPING SAID CEMENTITIOUS MIXTURES INTO SAID CHANNEL UNTIL SAID FLUID IS DISPLACED FROM SAID CHANNEL AND THE CEMENTITIOUS MIXTURE SUBSTANTIALLY FILLS THE CHANNEL; AND DELAYING SUBSEQUENT INJECTION OF SECONDARY RECOVERY FLUID INTO SAID FORMATION THROUGH SAID FIRST WELL BORE UNITL THE CEMENTITIOUS MIXTURE HAS HARDENED. 